Glass fibers are produced by the attenuation of molten glass issuing from nozzles under the influence of gravity. The nozzles are normally contained in an array on a bushing plate.
A bushing plate is normally fabricated of a precious metal alloy, nominally 80% platinum and 20% rhodium, to be able to withstand the extremely high processing temperatures of glass and the presence of corrosive agents in the bushing environment. A bushing plate has a limited service life, and must be repaired or reclaimed for re-use of the precious metal alloy.
The productivity or throughput of a bushing plate is a function of the number of nozzle tips contained in the array on the plate. The nozzle tips must be formed with uniform dimensions to ensure consistency of the diameter of the resultant glass fibers. The bushing plate through its high material cost, limited service life and accuracy requirements is a significant component of the cost of capital equipment used in glass fiber production.
A conventional bushing plate has tips formed with a constant diameter bore or aperture matched to the diameter of the glass fiber to be produced. As a result, each conventional bushing plate is specific to a predetermined glass fiber diameter, and separate tooling must be maintained for manufacture of variously sized bushing plates. A nozzle tip having a constant sidewall thickness is disclosed in terms of a modified Poiseuille equation in The Manufacturing Technology of Continuous Glass Fibers, 2nd ed. 1983 by K. L. Lowenstein @p.132.